Recently, with the rapid increase in the demand for portable electronic products such as notebooks, video cameras and cellular phones and the development of energy storage batteries, robots, satellites, etc. under active progress, numerous studies are being made on high-performance secondary batteries capable of being repeatedly charged and discharged.
Currently, nickel-cadmium batteries, nickel-hydrogen batteries, nickel-zinc batteries, lithium secondary batteries or the like are commercially available as secondary batteries. Among these, lithium secondary batteries are at the center of interest because they hardly have memory effects and can be freely charged or discharged in comparison with nickel-based secondary batteries. Advantageously, the lithium secondary batteries also exhibit very low self-discharge rate and high energy density.
Meanwhile, with the gradual exhaustion of carbon energies and the increased interest in the environment, the demands for hybrid and electric vehicles are increasing all around the world, including U.S.A, Europe, Japan and Korea. The hybrid or electric vehicles obtain driving force by means of energy charged and discharged in a battery pack, thereby eliminating or reducing an exhausted pollutant while ensuring excellent fuel efficiency compared to only engine-driven vehicles. Thus, the hybrid or electric vehicles better appeal to many consumers. Accordingly, the battery which is the most fundamental part in such hybrid or electric vehicles is the focus of many interests and studies.
The battery pack, particularly the battery pack used in electric vehicles has a plurality of battery modules to output high voltage, and the battery modules are connected by a connecting member called a bus bar. The bus bar should be strongly coupled with the battery modules therebetween so as to carry out electrical connection between the battery modules. Accordingly, the bus bar is coupled to the battery modules by a connecting member such as a bolt, nut or the like, and its coupling state is securely sustained.
However, since battery packs are generally used in devices and apparatuses that have frequent movement, there is a chance that the coupling state of the bus bar to the battery modules in the battery pack will loosen. For example, in the case of an electric vehicle in operation, the bus bar can loosen from the battery modules which will weaken the coupling state of the bus bar to the battery modules due to the impact and vibration applied to the battery pack. Furthermore, the loose coupling state of the bus bar only worsens over time, and unless artificially repaired, will not get any better.
Meanwhile, as the coupling state of the bus bar to the battery modules in the battery pack worsens, the resistance of the bus bar may increase causing the energy loss of the battery pack and heat generation, thereby leading to the overall temperature rise of the battery pack. This temperature rise of the battery pack may cause the performance degradation of the battery pack, as well as, in a severe case, the ignition or explosion thereof, which may induce a great problem on the stability of the battery pack.